1. Field of the Invention
The present invention relates to a high voltage DC power supplier and, more particularly, to a high voltage DC power supplied used for an electro-rheological (ER) fluid application units.
2. Description of the Background Art
In general, a strong electric field is to be formed in fluid in an ER fluid application unit to control a damping factor. The damping factor is adjusted by changing a strength of the electric field. Thus, in order to control the damping factor in the ER fluid application unit, a high voltage DC power supplier is needed to apply a strong electric field and vary a voltage.
The ER fluid application unit has capacitance load characteristics with an equivalent resistance and a capacitor component mixed therein. In order to obtain a fast transient response characteristics, a current should be supplied or cut off at a high speed so that electric charges can be charged quickly in the equivalent capacitor or already charged electric charges can be quickly discharged.
The equivalent resistance value of the ER fluid application unit varies depending on an applied voltage of both ends. That is, the equivalent resistance value is in inverse proportion to the applied voltage and exponentially changes. Accordingly, if the applied voltage is high, a resistance value is small and thus a high current flows. Meanwhile, if an applied voltage is xe2x80x980xe2x80x99, the resistance value is infinite and thus no current flows. This will now be described with reference to FIG. 1.
FIG. 1 is a circuit diagram of a high voltage DC power supplier in accordance with a conventional art.
As shown in FIG. 1, the high voltage DC power supplier includes: a transformer T1 for transforming an input voltage (Vs) to a high voltage of a certain level according to an electromagnetic induction operation, and outputting the transformed high voltage; a MOS transistor M1, a main switching device, for driving the transformer T1; and a diode D1 and a capacitor C1 for rectifying and smoothing the high voltage excited through secondary coil of the transformer T1 and supplying the smoothed voltage toward an ER fluid application unit.
The operation of the high voltage DC power supplier will now be described with reference to FIG. 2.
FIG. 2 is a graph showing discharge characteristics of an output voltage of FIG. 1.
First, the MOS transistor M1 is repeatedly turned on/off at a certain period by a controller (not shown). When the MOS transistor M1 is turned on, the input voltage (Vs) flows through the primary coil of the transformer T1 and the MOS transistor M1, according to which a high voltage with a certain level is excited in the secondary coil of the transformer T1.
The high voltage excited in the secondary coil of the transformer T1 is rectified by the diode D1 and smoothed by the capacitor C1, and an output voltage (Vo) of the capacitor C1 is supplied to the ER fluid application unit. The ER fluid application unit signifies an equivalent circuit 1 of the ER fluid application unit.
For reference, a ratio (Vo/Vs) of the input/output voltage is determined by a duty ratio of the MOS transistor M1 and a turn ratio of the primary and secondary coils of the transformer T1.
However, the high voltage DC power supplier with the structure as shown in FIG. 1 has a difficulty obtaining quick response characteristics when an output voltage (Vo) descends. The reason is because, in order to obtain quick response characteristics, the electric charges stored in the capacitors (C1, CL) should be quickly discharged when the output voltage (Vo) descends, but the electric charges are not transmitted to the secondary coil of the transformer T1 by the diode D1 and when the output voltage (Vo) is low, the resistance (RL) value is very high and thus the discharge time constant is increased. Therefore in the high voltage DC power supplier in accordance with the conventional art, since the output voltage (Vo) is gradually discharged as shown in FIG. 2, it fails to obtain a quick response characteristics.
As aforementioned, the conventional high voltage DC power supplier fails to obtain quick response characteristics since the voltage stored in the capacitor is gradually discharge when the output voltage descends in terms of the circuit characteristics.
Therefore, an object of the present invention is to provide a high voltage DC power supplier that is capable of quickly discharging a voltage stored in a capacitor by additionally installing a discharge circuit with a simple construction in an output stage of a high voltage DC power supplier and driving the discharge circuit at every discharge time point.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a high voltage DC power supplier including: a transformer driven by a switching device, transforming an input voltage to a certain level of high voltage, and outputting the transformed high voltage; a diode and a capacitor for rectifying and smoothing the high voltage outputted from the transformer, and supplying the smoothed voltage to an ER fluid application unit; a discharge circuit for forcibly discharging the output voltage when an output voltage of the capacitor descends; and a controller for controlling a turn-on operation of the switching device on the basis of a difference value between the output voltage and a reference voltage so that the output voltage can follow up a target voltage, and outputting a control signal for driving the discharge circuit to the discharge circuit when it reaches a discharge period.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.